1. Field of the Invention
The present invention relates to a toner developing an electrostatic latent image formed on an image bearer to visualize the electrostatic latent image in electrophotography, electrostatic recording and electrostatic printing, and to a developer, an image forming method and a process cartridge for an image forming apparatus using the toner.
2. Discussion of the Background
As disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publications Nos. 49-23910 and 43-24748, electrophotographic image forming methods typically include forming an electrostatic latent image on a photoreceptor made from photoconductive materials by various means; developing the latent image with a developer to form a visual image; optionally transferring the visual image onto a receiving material such as a paper; and fixing the image thereon upon application of heat, pressure or solvent vapor. A full-color image is formed of a black-colored toner, a yellow-colored toner, a magenta-colored toner and a cyan-colored toner.
The black-colored toner typically includes carbon black as a colorant. However, recently, a trial of using a fine powder of a black metallic compound as a colorant instead of the carbon black is suggested. Japanese Patent No. 2736680 discloses a mixture of solid solutions of Fe2TiO5 and Fe2O3—FeTiO3 having an average particle diameter of from 0.1 to 0.5 μm; Japanese Patents Nos. 3101782, 3108823 and 3174960 disclose a magnetic iron oxide including FeO by from 25 to 30%; Japanese Patents Nos. 3224774 and 3261088 disclose a magnetite having a residual magnetization not greater than6 emu/g; Japanese Laid-Open Patent Publication No. 2000-319021 discloses a particulate iron oxide having Ti inside and Ti and Fe on a surface thereof; Japanese Laid-Open Patent Publication No. 2002-129063 discloses a mixed phase crystal of a rutile type TiO2, which is coated with Fe2TiO4, and which has a saturated magnetization of from 0.5 to 10 emu/g and a particle diameter of from 0.1 to 0.4 μm; Japanese Laid-Open Patent Publication No. 2002-189313 discloses a metallic compound having a saturation magnetization not greater than 30 emu/g and a dielectric loss factor not greater than 50; and Japanese Laid-Open Patent Publication No. 2002-196528 discloses a colorant including a metallic compound having a saturation magnetization not greater than 40 emu/g in an amount not greater than 20 parts by weight.
A black metallic compound having high safety and good fluidity as a colorant has a higher heat conductivity than the carbon black, and therefore resultant toner has a lower-temperature fixability. In addition, the black metallic compound has a higher specific gravity than the carbon black, and therefore the resultant toner can easily be mixed with a carrier in a developer. However, a metallic compound is not well dispersed in a toner prepared by a pulverization method and does not fully exert the best performance.
Because of these reasons, a need exists for a toner including a well-dispersed colorant and producing images having less background fouling and high definition.